Electron multiplier having undulated passage with semiconductive secondary emissive coating



Aprnl 5, 1966 G. WOLFGANG 3,244,922

ELECTRON MULTIPLIER HAVING UNDULATED PASSAGE WITH SEMICONDUCTIVE SECONDARY EMISSIVE COATING Filed Nov. 5, 1962 3 Sheets-Sheet 1 IO l2 3o 45 78 I8 48 32 Z A6 /I\ 60 68 INVENTOR.

LOZU RE G. WOLFGANG a /m0, EM) W ATTORNEYS Apnl 5, 1966 G. WOLFGANG 3,244,922

ELECTRON MULTIPLIER HAVING UNDULATED PASSAGE WITH SEMICONDUCTIVE SECONDARY EMISSIVE COATING Filed Nov. 5, 1962 3 Sheets-Sheet 2 INVENTOR. LOZURE G. WOLFGANG ATTORNEYS APr11 1956 L. e. WOLFGANG 3,244,922

ELECTRON MULTIPLIER HAVING UNDULATED PASSAGE WITH SEMICONDUCTIVE SECONDARY EMISSIVE COATING Filed Nov. 5, 1962 3 Sheets-Sheet 3 INVENTOR. LOZURE G. WOLFGANG il/m, amma;

ATTORNEYS United States Patent Oflice 3,244,922 Patented Apr. 5, 1966 3,244,922 ELECTRON MULTIPLIER HAVING UNDULATED PASSAGE WITH SEMICONDUCTIV E SECOND- ARY EMISSIVE CGATIN G Lozure G. Wolfgang, Fort Wayne, Ind., assignor to International Telephone and Telegraph Corporation, Nutley, N.J., a corporation of Maryland Filed Nov. 5, 1962, Ser. No. 235,218 16 Claims. (Cl. 313-95) This invention relates to electron multiplier devices and to the dynode elements therefor.

Conventional electron multipliers comprise a plurality of discreet stages or dynodes operated at monotonically increasing potentials. The dynodes are formed of or coated with secondary emissive material and arranged so that electrons injected into the low potential end of the device are multiplied upon dynode impact, thus resulting in secondaries being accelerated to a succeeding dynode at which the process recurs hence giving rise to overall cascade multiplication of electrons. An electron multiplier is commonly enclosed in an evacuated envelope and the progressively increasing potentials are normally obtained from an external resistance divider network and applied to the dynodes through a multi-lead stem. This construction which involves independent and electrically isolated mounting of each of the dynodes is complex and thus costly, and further, the construction is fragile and thus not well suited for airborne applications.

It has been proposed to reduce the number of external leads to an electron multiplier by incorporating the resistance divider within the envolpe. However, such an arrangement does not eliminate the complexity of separately mounting the dynodes or reduce the fragility of the tube. wherein a trochoidal-like trajectory for the electrons from dynode to dynode is provided by a transverse magnetic field provided by an external magnet. It has further been proposed to employ in such an electron multiplier, in lieu of individual dynodes, an elongated semi-conductive resistance strip with the requisite potential diiference being applied to the ends thus providing a continuous potential distribution along the dynode strip. Such a construction while greatly simplifying the structure and eliminating the multiple external leads, requires a heavy external magnet to generate the cross field. Therefore it is desirable to provide an electron multiplier construction of the semi-conductive strip variety wherein the desired electron trajectories are provided electrostatically rather than by combined magnetic and electric fields.

It is accordingly an object of the invention to provide an improved electron multiplier.

Another object of the invention is to provide an improved dynode element for an electron multiplier.

A further object of the invention is to provide an improved electron multiplier and dynode element therefor employing a semi-conductive dynode strip wherein the desired electron trajectories are provided electrostatically.

The objects of the invention are obtained by providing a dynode element comprising means formed of dielectric material defining an elongated tubular passage having a plurality of undulations therein, the passage having an elongated continuous coating of semi-conductive secondary-emissive material formed on its interior surface.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of the preferred em- Electron multipliers have also been proposed bodiment of the invention incorporated in a photomultiplier;

FIG. 2 is a fragmentary exploded perspective view further illustrating the dynode element of FIG. 1;

FIG. 3 is a fragmentary cross-sectional view illustrating a modification of the invention;

FIG. 4 is a fragmentary cross-sectional view showing a modified terminal and target electrode arrangement;

FIG. 5 is a fragmentary cross-sectional view illustrating another form of target electrode;

FIG. 6 is a fragmentary cross-sectional view illustrating yet another form of target electrode;

FIG. 7 is a fragmentary exploded view in perspective illustrating another embodiment of the invention;

FIG. 8 is a cross-sectional view illustrating still another embodiment of the invention; and

FIG. 9 is a top view of the embodiment of FIG. 8.

Referring now to FIGS. 1 and 2 of the drawing, there is shown a photomultiplier, generally indicated at 10, comprising a dynode element 12 having a photocathode assembly 14 sealed to one end thereof and a target electrode 16 sealed to the other end.

The dynode element 12 comprises a pair of generally rectangular blocks 18 and 20 formed of suitable dielectric material, such as a high alumina ceramic material. Blocks 18 and 20 respectively have abutting fiat surfaces 22 and 24. The flat surfaces 22 and 24 respectively have mating elongated channels 26 and 28 formed therein extending longitudinally from one end 30 to the other end 32 of the dynode element 12. In the illustrated embodiment, the side walls 34, 36 of the channels 26, 28 are straight and parallel, however, the bottom walls 38 have a plurality of uniform, generally sinusoidal undulations therein; it Will be seen that the undulations lie in a plane perpendicular to the plane of the fiat surfaces 22, 24. It will be seen with reference to FIG. 1, that the undulations formed in the blocks 18, 20 are in phase so that the passage 40 define-d by the two channels 26, 28 has a uniform rectangular cross-section from end 30 to end 32 of dynode element 12.

Suitable grooves 42, 44 are formed in the walls of channels 26, 28 respectively adjacent ends 30, 32 for accommodating conductive terminals 46, 48 to which external leads 50, 52 are respectively connected. In accordance with the invention, the walls 34, 36 and 38 of the channels 26, 28 have a relatively thin layer or coating 54, 56 of secondary-emissive resistive material deposited thereon extending between the terminals 46, 48. Suitable materials which may be deposited by vapor deposition, include lithium fiuoride (LiF) or barium fluoride (BaF to which impurities, such as chromium, arsenic or germanium, are added to reduce the resistance, as is well known to those skilled in the art.

It will now be seen that if a potential difference is applied to the leads 50, 52, that difference will result in a continuous potential distribution along the coatings or dynode strips 54, 56 between terminals 46, 4-8. Thus, if a potential of +100 volts is applied to lead and a potential of +1000 volts is applied to lead 52, the potential difference of 900 volts will be distributed uniformly along the dynode strips 54, 56 between terminals 46, 48.

In the illustrated embodiment, the flat surfaces 22, 24 of the blocks 18, 20 are sealed together in any conven tional manner. The photocathode assembly 14 comprises a glass plate 58 sealed to the end 30 of the dynode element 12 and having a conventional photocathode 60 formed on its interior surface in the entrance 62 of the passage 40 defined by the channels 26, 28. An external lead 64- is connected to the photocathode 60 in order to connect the same to a suitable source of potential such as ground.

Target electrode 16 is a metal plate sealed to the other end 32 of the dynode element 12 and closing the other end 66 of the passage 40, the passage being evacuated during the assembly operation. Target electrode 16 is connected to a suitable source of potential, such as +1100 volts by a load resistor 68 and is connected to an output circuit by a suitable coupling capacitor 72.

It will now be seen' that when input radiation, as indicated by the arrow 74, impinges on thephotocathode 6t electrons will be emitted which will be accelerated by the potential distribution along the dynode strips 54', 56 in a trajectory as shownby the dashed lines '76, thereby providing cascade multiplication of electrons. The multiplied electron flow will ultimately be attracted to the electrode 16 thus providing an output signal in the output circuit 701" While the dynode element 12 of FIG. 1 is shown as having three undulations formedin the passage 48, it will be readily understood that a greater number such as ten will ordinarily be provided. In specific embodiment, the blocks 18,20 may be two to three inches long, the cha'n nels 2 6 28 may be from one half inch to one inch Wide and from one eighth inch to one quarter inch deep thus providing a passage 40 having a uniform height of one: hah inch. It will be readily seen that the channels 26, 28 may be conveniently cast in the blocks 18, 20.

Referring now to FIGURE 3 in which like elements are indicated by like" reference numerals, in order to provide a field plot which tends to form: the electron trajectories so that they strike predominately in the valleys 78, it is: desirable that the potential distribution along the semiconductive coating be non-linear and preferably such that the potential gradient along the strip be reduced in the valleys. This maybe accomplished by providing conductive or low resistivity strips 32, 84 of high secondary emission yield over the dynode material 54, 56 in the valleys 78, 80' as shown' Similarly, the desired trajectories may be achieved by providing the conductive or low resistivity strips 82, 84 under the dynode material 54 56 in the valleys 78; 80 in which case the secondary yield of the material is of lesser importance, or by thickening the dynode strip in the valleys 78, 88.

Referring now to FIG. 4, the dynode element 12 maybe included Within an evacuated envelope, or may be employed in satellite instrumentation where evacuation is unnecessary. In this embodiment, the high potential terminal for the dynode strips 54, 56 may be plated on the end 32 of blocks 18'," 20,- as at 86 and with target electrode 88 facing" end 66 of passage 40, but being exterior thereto, as shown.

Referring now to FIG. 5, target electrode 90 may be sealed in suitable grooves 92 and in end 66 of the channels 26, 28, as shown.

Referring now to FIG. 6, end 32 of blocks 18, ZQ'may have portions 94, 96 integrally formed thereon and closing' end 66 of passage 40 and the target elect-rode 98 may be arranged within end 62 of passage 40 and abutting por-' tions 94, 96, as shown. w I

Referring nowto FIG. 7, the undulated passage may be formed in the surface of only one of the blocks rather than in both blocks as in the previous embodiments. Here, block 189 of dielectric material is provided having a flat surface 102 in which channel 104 is formed. Channel 104' has a flat bottom wall 106 and equally spaced undulate'd sidewalls 108 and 110:. A' fiat top plate 112 of dielectric material is ranged in abutting relationship with flat surface 102 of block thus closing channel 104 to define the elongated undulat'ed passage. It will be seen that in this embodiment, the undulations lie in the plane of surface 102 rather than perpendicular thereto as in the case of the previous embodiments.

It will be readily understood that it is the undulated side walls 108 and of channel 104 which provide the desired trajectory for the electrons and thus, as a minimum, only the undulated Walls need have the coating of secondary-'emissive dynode material deposited thereon.

However, it is simpler and, in fact, considered desirable to coat all of the Walls of the undulated passage with secondary-emissive dynode material.

It will be readily understood that the proportioning of the undulated passage of the embodiment of FIG. 7 together with the means for injecting electrons into the low potential end, and'the target electrode arrangements at the high potential end may be the same as those shown in connection with FIGS. 1 through 6 inclusive.

Referring now to FIGS. 8 and 9, the dynode element 114 may in accordance with the invention take the form of an elongated glass or ceramic tube 116 having uniform generally sinusoidal undulations formed therein in one plane, as shown. Here, the interior wall of the tube 116 is coated with seco'ndary-ernissive dynode material, as at 118 with conductive terminals 120, 122 being provided at the ends of the tube 116' for applying a potential difierence across the ends of the conductive coating 118.

It will now be readily seen that the electron multiplier and dynode element thereforof the invention, is characterized by its ruggedness, simplicity, ease of construction and assembly, minimum number of external leads, size and eiiiciency.

While I have described above the principles of my invention in connection withspecific apparatus, it is to be clearly understood that this description is made only by Way of example and not as a limitation to the scope of my invention.

What is claimed is:

1. In an electron multiplied device, a dynode element comprising a block of dielectric material, an elongated tubular passage throughsaid block between two ends thereof and having a plurality of undulations on the interior walls, said passage having an elongated continuous coating of semi-conductive secondary-emissive material onthe surface of said walls.

2'. The device or" claim 1 wherein said undulations are in one plane.

3. The device of claim 1 further comprising terminal means respectively connected to said coating adjacent the ends thereof for applying a potential difference between said ends whereby electrons injected into one end of said passage are accelerated toward the other end and cascade multiplied.

4'. The deviceor claim 1 further comprising terminal means respectively connected to said coating adjacent the end thereof for applying a potential difference between said ends whereby electrons injected into one end of said passage are accelerated toward the other end, and where in said undulations are symmetrical and in one plane and proportioned so that said electrons are cascade multi plied during their travel from said one end of said passage to the other, I v I 5. The device of claim 1 wherein said passage is rectangular in cross section.

6. The device of claim 1 wherein said block comprises a pair of members respectively having flat abutting surfaces, at least one of said abutting surfaces having an elongated channel formedthere'in'which defines said passage.

7. The device of claim 1 wherein said means comprises a pair of blocks respectively havingflat abutting surfaces,- said surfac'es respectively having mating elongated channels formed therein Which mutually define said passage.

8. The device of claim '7 wherein said passage is of uniform rectangular cross-section and wherein said undulations are in a plane perpendicular to said surfaces.

9. The device of claim 3 wherein said passage is of uniform cross-section, wherein said undulations are in one plane and generally sinusoidal in configuration thereby defining successive peaks and valleys on opposite surfaces of said passage, and further comprising means providing a non-linear distribution along said semiconductor coating for reducing the'potential' gradient in said valleys to cause said electrons to strike predominantly therein.

10. The device of claim 1 wherein said means comprises a block having a flat surface with an elongated channel formed therein of uniform rectangular crosssection which defines three sides of said passage, and a flat plate abutting said surface and forming the fourth side of said passage, said undulations being in the plane of said surface.

11. An electron multiplier device comprising: a dynode element including a block of dielectric material, an elongated tubular passage of uniform cross-section through said block between two ends thereof and having a plurality of undulations on the interior walls, said undulations being in one plane and generally sinusoidal in configuration, said passage having an elongated continuous coating of semi-conductive secondary-eniissive material on the surface of said walls; terminal means respectively connected to said coating adjacent the ends of said passage for applying a potential difference between the extremities of said coating whereby an increasing potential is provided along said coating from one end of said passage to the other; means for injecting electrons into said one end of said passage whereby said electrons are accelerated toward the other end by said increasing potential, said undulations being proportioned so that said electrons are cascade multiplied during their travel from one end of said passage to the other; and target electrode means adjacent said other end of said passage.

12. The device of claim 11 wherein said target electrode sealingly closes said other end of said passage.

13. The device of claim 11 wherein said electron injecting means comprises photocathode means sealingly closing said one end of said passage.

14. The device of claim 11 wherein said electron injecting means comprises photocathode means sealingly closing said one end of said passage, and wherein said target electrode sealingly closes said other end of said passage, said passage being evacuated.

15. An electron multiplier device comprising a dynode element including a pair of generally rectangular blocks formed of dielectric material respectively having flat abutting surfaces, the abutting surface of at least one of said blocks having an elongated channel formed therein extending from one end thereof to the other, the other of said members closing said channel to define an elongated passage, said passage being of uniform rectangular cross-section, two opposite side Walls of said passage respectively having a plurality of generally sinusoidal undulations therein; at least said opposite side walls of said passage respectively having an elongated continuous coating of semi-conductive secondary-emissive material formed thereon respectively extending to adjacent the ends of said passage; terminal means in said passage respectively adjacent the ends thereof and connected to said coating for applying a potential difference between the ends of said coating whereby an increasing potential is provided along said coating from one end of said passage to the other; means for injecting electrons into said one end of said passage whereby said electrons are accelerated toward the other end by said increasing potential, said undulations being proportioned so that said electrons are cascade multiplied during their travel from one end of said passage to the other; and target electrode means adjacent said other end of said passage.

16. The device of claim 15 wherein said members are sealed together, wherein said electron injecting means comprises a transparent plate sealed to one end of said members and closing said one end of said passage, said plate having photocathode means thereon in said one end of said passage, and wherein said target electrode means sealingly closes said other end of said passage.

References Cited by the Examiner UNITED STATES PATENTS 2,207,356 7/ 1940 Pierce 313104 2,232,900 2/1941 Brewer 313105 2,841,729 7/1958 Wiley 3l3l04 FOREIGN PATENTS 901,088 1/1954 Germany. 118,814 5/1947 Sweden.

GEORGE N. WESTBY, Primary Examiner.

ARTHUR GAUSS, Examiner.

C. Q. GARDNER, R. SEGAL, Assiian Examiners, 

1. IN AN ELECTRON MULTIPLIED DEVICE, A DYNODE ELEMENT COMPRISING A BLOCK OF DIELECTRIC MATERIAL, AN ELONGATED TUBULAR PASSAGE THROUGH SAID BLOCK BETWEEN TWO ENDS THEREOF AND HAVING A PLURALITY OF UNDULATIONS ON THE INTERIOR WALLS, SAID PASSAGE HAVING AN ELONGATED CONTINUOUS COATING OF SEMI-CONDUCTIVE SECONDARY-EMISSIVE MATERIAL ON THE SURFACE OF SAID WALLS. 